Add support for application_start_module

This is an optional value within [erlang] in the gleam.toml file.
It will be used for the `mod` value when generating a .app file

Author: Rodrigo Álvarez

lib/mix/lib/mix/dep/loader.ex

@@ -367,19 +367,30 @@ defmodule Mix.Dep.Loader do
     {dep, []}
   end
 
-  defp gleam_dep(%Mix.Dep{opts: opts} = dep, children, locked?) do
+  defp gleam_dep(%Mix.Dep{opts: opts} = dep, _children = nil, locked?) do
     Mix.Gleam.require!()
 
-    deps =
-      if children do
-        Enum.map(children, &to_dep(&1, opts[:dest], _manager = nil, locked?))
-      else
-        config = File.cd!(opts[:dest], fn -> Mix.Gleam.load_config(".") end)
-        from = Path.join(opts[:dest], "gleam.toml")
-        Enum.map(config[:deps], &to_dep(&1, from, _manager = nil, locked?))
-      end
+    config = File.cd!(opts[:dest], fn -> Mix.Gleam.load_config(".") end)
+    from = Path.join(opts[:dest], "gleam.toml")
+    deps = Enum.map(config[:deps], &to_dep(&1, from, _manager = nil, locked?))
+
+    properties = [
+      {:vsn, to_charlist(config[:version])},
+      {:mod, {String.to_atom(config[:mod]), []}}
+    ]
 
-    {%{dep | opts: Keyword.merge(opts, app: false, override: true)}, deps}
+    contents = :io_lib.format("~p.~n", [{:application, dep.app, properties}])
+
+    [opts[:build], "ebin", "#{dep.app}.app"]
+    |> Path.join()
+    |> File.write!(IO.chardata_to_string(contents))
+
+    {dep, deps}
+  end
+
+  defp gleam_dep(%Mix.Dep{opts: opts} = dep, children, locked?) do
+    dep = %{dep | opts: Keyword.merge(opts, app: false, override: true)}
+    {dep, Enum.map(children, &to_dep(&1, opts[:dest], _manager = nil, locked?))}
   end
 
   defp mix_children(config, locked?, opts) do

lib/mix/lib/mix/gleam.ex

@@ -24,7 +24,8 @@ defmodule Mix.Gleam do
         version: Map.fetch!(json, "version"),
         deps: deps ++ dev_deps
       }
-      |> maybe_gleam_version(json["gleam"])
+      |> maybe_gleam_version(json)
+      |> maybe_application_start_module(json)
     rescue
       KeyError ->
         Mix.raise("Command \"gleam export package-info\" unexpected format: \n" <> json)
@@ -55,10 +56,18 @@ defmodule Mix.Gleam do
     end
   end
 
-  defp maybe_gleam_version(config, nil), do: config
+  defp maybe_gleam_version(config, json) do
+    case json["gleam"] do
+      nil -> config
+      version -> Map.put(config, :gleam, version)
+    end
+  end
 
-  defp maybe_gleam_version(config, version) do
-    Map.put(config, :gleam, version)
+  defp maybe_application_start_module(config, json) do
+    case get_in(json, ["erlang", "application_start_module"]) do
+      nil -> config
+      mod -> Map.put(config, :mod, mod)
+    end
   end
 
   def require!() do

lib/mix/test/mix/gleam_test.exs

@@ -49,7 +49,12 @@ defmodule Mix.GleamTest do
             "gleam_stdlib" => %{"version" => ">= 0.18.0 and < 2.0.0"},
             "my_other_project" => %{"path" => "../my_other_project"}
           },
-          "dev-dependencies" => %{"gleeunit" => %{"version" => ">= 1.0.0 and < 2.0.0"}}
+          "dev-dependencies" => %{
+            "gleeunit" => %{"version" => ">= 1.0.0 and < 2.0.0"}
+          },
+          "erlang" => %{
+            "application_start_module" => "some@application"
+          }
         }
         |> Mix.Gleam.parse_config()
 
@@ -62,7 +67,8 @@ defmodule Mix.GleamTest do
                  {:gleam_stdlib, ">= 0.18.0 and < 2.0.0"},
                  {:my_other_project, path: "../my_other_project"},
                  {:gleeunit, ">= 1.0.0 and < 2.0.0", only: :dev}
-               ]
+               ],
+               mod: "some@application"
              }
     end
   end